Multiple layer preform

ABSTRACT

An injection molding process for making a multiple layer, plastic structure. A plastic sleeve is placed and then enclosed in a mold cavity. A flowing heated plastic is conducted into the mold cavity, radially inside the sleeve, and forced radially outward against the sleeve. The flowing plastic forces the sleeve outward and forms, with the sleeve, an integrally bonded laminated structure. The mold is opened and the plastic structure is removed, and this structure may then be reformed to form a container particularly suitable for containing beverages, foods, cosmetics, pharmaceuticals and chemicals.

This is a divisional of application Ser. No. 08/137,888, filed Oct. 15,1993, now U.S. Pat. No. 5,443,767, which is a continuation of Ser. No.07/951,319, filed Sep. 25, 1992, now abandoned, which is a continuationof Ser. No. 07/546,093, filed Jun. 29, 1990, now abandoned, which is adivisional of Ser. No. 07/238,979, filed Aug. 25, 1988, now U.S. Pat.No. 4,942,008, which is a continuation of Ser. No. 06/753,402, filedJul. 10, 1985, now abandoned.

BACKGROUND OF THE INVENTION

This invention generally relates to processes for manufacturing plasticstructures and to containers made from those structures. Morespecifically, the invention relates to a process for manufacturinglaminated plastic structures via an injection molding process and tocontainers, especially well suited for holding carbonated beverages,foods and chemicals, made from those plastic structures.

Plastic containers are often used to hold carbonated beverages, and infact, their use for this purpose has steadily grown over the past fewyears. While many plastics may be used for carbonated beveragecontainers, polyethylene terephthalate (referred to herein as PET) hasachieved a major role in this area because, when manufactured properly,it has many desirable characteristics such as low cost, light weight,durability and rigidity.

Most of the excellent physical properties of PET become evident onlywhen the resin is stretch-molded into a bi-axially oriented condition,and the majority of PET bottles produced for carbonated beverages aremanufactured by, first, molding a PET preform via an injection moldingprocess, and second, reforming the preform into the final desired shape.With most PET containers a different machine is employed in each ofthese two manufacturing steps; however, a significant number ofbi-axially oriented PET bottles are also formed in one apparatus havinga plurality of positions or stations. Some PET containers not requiringhigh mechanical properties are produced via conventional injection blowmolding and have little or no molecular orientation.

The major cost element in the manufacture of PET bottles is the cost ofthe PET resin itself. Accordingly, PET bottle suppliers are interestedin decreasing the amount of PET resin in the bottles, and one way ofdoing this is to reduce the thickness of the walls of the bottles. Thereare lower limits, though, on the thickness of the sidewalls of PETbottles. In particular, PET is gas permeable; and when used to hold acarbonated beverage, the sidewalls of a PET bottle must be thicker thancertain minimum sizes if the bottle is to meet industry standardsrelating to carbon dioxide retention levels. For example, as defined bythe industry, the term "shelf life" for a carbonated beverage bottle isthe time, in weeks, for the beverage to lose 15 percent of its originalcarbonation level, when stored at room temperature. The major carbonatedsoft drink manufacturers in the United States have established arequirement that a PET bottle larger than one liter, when used topackage a carbonated soft drink, must have a shelf life of 16 weeks.Bottles less than one liter generally have had to compromise on a shelflife of about ten weeks.

One way to reduce the amount of PET in a bottle and also extend theshelf life thereof, is to use a laminated structure, where the bottlecomprises a first layer formed from PET and a second layer formed from amaterial which has a very low gas permeability (referred to herein as ahigh gas barrier material).

The use of a laminated bottle structure is advantageous for otherreasons as well. For instance, it is highly desirable to employ usedplastic material in beverage containers. Such a use, first, wouldprovide a productive outlet for the large number of plastic bottles thatare currently simply discarded, and second, would reduce the cost of thematerials needed to manufacture new bottles. Government regulations,however, do not allow reprocessed plastic to come into contact withproducts stored in beverage containers and, instead, require that onlyunused plastic materials come into contact with those products. One wayto meet these regulations while still using reprocessed plastics in abeverage container is to form the container from a laminated structurewith a first, outer layer made from the reprocessed material and asecond, inner layer made from unused plastic material.

While there are several ways to form a bottle with a laminatedstructure, it is very desirable to use an injection molding process.Such a process, first, would require relatively few changes to thepresent processes used by many in the industry and thus could be readilyadapted thereby, and second, would have the typical advantagesassociated with injection molding processes such as dimensionalprecision and high productivity. Heretofore, however, the art has notbeen able to develop a practical, efficient and cost-effective injectionmolding process for manufacturing large numbers of laminated PETbottles.

In part, this is due to the fact that with typical injection moldingprocesses used to make plastic preforms, as a practical matter, it isnecessary to make the preform with a slight axial taper. This taperallows the mold to open and permits the preform to be removed therefromwithout breaking or tearing the preform. For example, with a prior artmethod of making a laminated, plastic preform using an injection moldingprocess, a first plastic material is cut, preshaped into a tapered formand placed on a mold core rod. Then, a second, liquid plastic isinjected around that rod, and the first and second plastic materialsbond together to form the laminated structure. Because of the time andexpense needed to preshape the first material into the desired, taperedform and to place it over the core rod of the mold, this general type ofmethod is not believed to be a practical way to manufacture largenumbers of plastic preforms. This process also results in the preshapedmaterial being on the inside wall of the formed structure.

SUMMARY OF THE INVENTION

The general object of the present invention is to provide an improvedinjection molding process for making laminated plastic structures andpreforms.

A more specific object of this invention is to use a plastic sleeve inan injection molding process to form one or more layers of a laminatedplastic preform without deforming the shape of the sleeve prior toplacing the material in the mold and without requiring separate specificsteps to shape the sleeve into a tapered form.

These and other objects are attained with an injection molding processfor making a multiple layer plastic structure comprising the steps ofplacing a plastic sleeve in a mold, and closing the mold to enclose thesleeve in a mold cavity. A flowing, heated plastic is conducted into themold cavity, and forced radially outward against the sleeve. The flowingplastic forces the sleeve outward, for example into an outwardly taperedshape, and forms, with the sleeve, an integrally bonded laminatedstructure. Once that structure is made, the mold is opened, and thestructure is removed therefrom and if desired, reformed to form acontainer. The container so made comprises neck, side wall and bottomportions connected together to form a one-piece bottle. The side wallportion includes outside and inside layers, while the neck and bottomportions of the container consist of a single plastic material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side, cross-sectional view of a plastic preform made inaccordance with the present invention.

FIG. 2 is an axial cross-section through a mold which may be employed tomanufacture the preform shown in FIG. 1.

FIG. 3 is a perspective view of a tube from which a sleeve may be cutand then used to make an outer layer of the preform shown in FIG. 1.

FIG. 4 is a side view of a bottle made from the preform illustrated inFIG. 1.

FIG. 5 is an enlarged view of a portion of the mold shown in FIG. 2.

FIG. 6 is an enlarged view of another portion of the mold shown in FIG.2, exaggerating the space between the sleeve placed therein and theadjacent surfaces of the mold.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows laminated preform 10 having a generally U-shapedcross-section and comprising side portion 12, bottom portion 14 and neckportion 16. Side portion 12 includes outer layer 20 and inner layer 22that have been integrally bonded or fused together in the processdescribed below. Bottom and neck portions 14 and 16, however, are notlaminated and, instead, are each formed or consist of a single plasticmaterial. As is conventional, neck portion 16 includes one or morethreads 24 provided to receive a bottle cap after preform 10 has beenexpanded to form a container and the container has been filled with abeverage.

FIG. 2 illustrates mold 26 for making preform 10. Mold 26 includes maleand female subassemblies; and, in turn, the female subassembly comprisesoutside mold base 30, inside cavity block 32, end cap 34, and upperthread splits 36, and the male subassembly of mold 26 includes elongatedrod 40 and support piece 42. Thread splits 36, cavity block 32, and endcap 34 form a cavity 44 in mold 26, and end cap 34 has a gate 46 forconducting liquid plastic into that cavity. FIG. 2 shows mold 26 in aclosed position, wherein rod 40 extends into mold cavity 44. The shapeof mold cavity 44 determines the shape of preform 10, and the moldcavity includes side, bottom, and neck portions that are used to formside wall 12, bottom 14, and neck 16 of the preform. As is conventional,mold 26 may be opened by moving apart the male and female subassembliesof the mold and removing rod 40 from cavity 44 of the mold.

Mold 26 is provided with suitable cooling fluid passages to ensureproper temperature control of the mold and the preform made therein. Tofacilitate opening mold 26 after a preform has been made therein, and toassist removing the preform from mold cavity 44, the substantiallyaxially extending surface 52 of cavity block 32 and the opposing surface54 of rod 40 slightly taper upwardly outwardly.

FIG. 3 shows plastic tube 60 from which a sleeve 62 may be cut and thenused to form outer layer 20 of the preform 10. To manufacture preform10, sleeve 62 is cut from tube 60 and placed in the cavity 44 of mold26, closely adjacent surface 52 of cavity block 32. This is done, itshould be noted, when mold 26 is open--that is, prior to inserting rod40 into mold cavity 44. Once plastic sleeve 62 is properly located inmold cavity 44, rod 40 is inserted thereinto and a flowing plasticmaterial is injected into the mold cavity, via gate 46, radially insidethe plastic sleeve. The plastic injected into cavity 44 via gate 46 isin a heated, liquid, pressurized state, and the heat and pressure ofthis plastic heats plastic sleeve 62 and forces that sleeve outward,into a shape conforming with the shape of the adjacent surface 52 ofcavity block 32--that is, into a shape slightly tapering upwardlyoutwardly. At the same time, the heat and pressure of the liquid plasticalso causes sleeve 62 to change into a plasticized state whereupon theliquid plastic fuses therewith to form an integrally bonded, laminatedstructure. After mold cavity 44 is filled, it is cooled to solidifypreform 10, and mold 26 is opened and preform 10 is removed therefrom.

With an alternate procedure, molten PET may be flowed into cavity 44, tofill the cavity partially, before rod 40 is inserted thereinto. This maybe done either prior to or after placing sleeve 62 in mold cavity 44,although it is believed preferable to conduct the flowing plastic intothe mold cavity after the sleeve 62 is placed therin. In either case,once mold cavity 44 is partially filled with the molten PET and sleeve62 is properly located in the mold cavity, mold 26 is closed and rod 40is inserted into the mold cavity, forcing the molten PET radiallyoutward against sleeve 62 to push that sleeve into the desired taperedshape and to make preform 10.

Thus, in accordance with the present invention with either of theabove-discussed procedures, a laminated preform 10 is made using apre-made plastic sleeve 62 to form an outside layer 20 of that preform,and it is not necessary to perform any specific, separate steps oroperations on that sleeve to provide it with the desired, tapered shapein mold 26.

After being removed from mold 26, preform 10 is expanded to form bottle64, shown in FIG. 4. The upper and lower edges of the layer of bottle 64formed from tubular segment 62 are shown as 62a and 62b, respectively,in FIG. 4. Preform 10 may be expanded into bottle 64 in any suitableway. For example, in accordance with one conventional process, preform10 is reheated, inserted into a second mold cavity, which conforms tothe shape of the finished bottle 64, and then expanded outward againstthe surfaces of the second mold cavity by means of a pressurized fluidforced into the preform. This technique and others for expanding preform10 are very well known in the field.

Also, it should be noted that preform 10 is heated and cooled duringdifferent stages of the process in which it is formed and expanded intobottle 64, and sleeve 62 may also be cooled or heated prior to insertioninto mold cavity 44. Any suitable technique or techniques may be used tocontrol the temperatures of preform 10 and sleeve 62, and numerous suchmethods are very well known to those skilled in the art.

Preferably, again with reference to FIG. 2, sleeve 62 is held axiallystationary within mold cavity 44 as liquid plastic is forced against thesleeve. This may be done in several ways. For example, sleeve 62 may beforced into cavity 44 of mold 26, in a tight pressure fit againstsurface 52 of cavity block 32, and this pressure fit, by itself, may beused to hold the sleeve 62 stationary as the liquid plastic is forcedagainst the sleeve. Alternately, mold 26 may include one or moreshoulders (not shown) projecting slightly into cavity 44 to hold sleeve62 in place. Such shoulders may extend into mold cavity 44 from lowerportions of thread splits 36, for example. If this latter arrangement isemployed to hold sleeve 62 in place in mold cavity 44, these shouldersare moved away from preform 10 prior to removing the preform from mold26.

With reference to FIG. 5, as liquid plastic is injected into mold cavity44, the plastic tends to move upward, past the bottom of sleeve 62,before completely filling the space 66 immediately and directly belowbottom edge 70 of the sleeve. Preferably, means are provided in mold 26to vent air radially outward, away from mold cavity 44, from space 66 toallow the liquid plastic to flow into and eventually fill that space.Special apertures may be formed in mold 26 extending into communicationwith space 66 to vent air therefrom. Alternately, air in space 66 may bevented therefrom simply through an interface formed by two or morepieces of mold 26, and which is in communication with the space directlybelow edge 70.

With reference to FIG. 6, as the liquid plastic is injected into moldcavity 44, the plastic may move upward past the top edge of sleeve 62,before the sleeve expands outward to lie fully against the adjacentsurface 52 of mold 26. Mold 26 may further include means to vent airradially outward, away from mold cavity 44, from the space 72 that isradially outside sleeve 62. This venting means allows sleeve 62 toexpand into space 72 without requiring that the air therein pass throughthe liquid plastic material itself. Here too, special apertures may beformed in mold 26 extending into communication with space 72, or airfrom that space may be vented through an interface formed by two or moreof the pieces forming the female subassembly of mold 26, for instancethrough the interface formed by thread splits 36 and inside cavity block32.

Sleeve 62, from which outer layer 20 of preform 10 is made, may itselfbe made of various materials or multiple materials. For instance, thetube may be made from a material having a very low gas permeability, forexample, a material comprising a diacid component comprisingthiobis(p-phenyleneoxy)!diacetic acid,sulfonylbis(p-phenyleneoxy!diacetic acid, and mixtures thereof orpolyesters blended with bisphenols. The use of such a material for outerlayer 20 of preform 10 would enable a plastic bottle to be formed havinga low gas permeability and with a reduced side wall thickness and,hence, a reduced total amount of material. Also, sleeve 62 may be madeor formed from recycled material such as PET. With the process of thepresent invention, the inside surfaces of sleeve 62 are completelycovered by the liquid plastic injected into mold 26 so that sleeve 62itself will not come into contact with any product held in a containermade from preform 10.

Sleeve 62 may be made in several ways and may comprise one or morelayers of plastic. For example, as explained above, sleeve 62 may be cutfrom tube 60 which may be a mono layer plastic, or a multi-layercoextrusion. Preferably, tube 60 is formed by extrusion through a die,but it can be formed by other techniques such as by winding a sheet ofplastic on a mandrel. Examples of multi-layer compositions are:reclaimed PET on a high gas barrier polyester:polypropylene/adhesive/ethylene vinyl alcohol co-polymer/adhesive;PET/adhesive/ethylene vinyl alcohol co-polymer/adhesive; Acrylonitrileco-polymer/adhesive; Polycarbonate/high barrier polyester;Polyamides/adhesives; and Polycarbonate/Polyetherimide.

For applications such as holding carbon dioxide inside a package, it isadvantageous to have the layers of sleeve 62 integrally bonded together.However, in many applications where sleeve 62 is used to reduce thepermeation of oxygen into a container, such as food packaging, a tightmechanical fit between layers of the sleeve is adequate. As shown inFIG. 3, sleeve 62 has a uniform circular cross section, but the sleevemay have any suitable shape.

In particular, the lower portion of sleeve 62 may slant radiallyinwardly, forming a conically shaped portion, or the lower portion ofthe sleeve may curve radially inwardly. Regardless of the specific shapeof sleeve 62, when the sleeve is used with a mold where the heatedplastic is injected into the mold via a gate located below the sleeve,preferably the sleeve has a lower or bottom opening to conduct thatheated plastic into the interior of the sleeve. Sleeve 62 may be cutfrom tube 60 in any acceptable manner, or the sleeve may be formed witha shape and size appropriate for use in the present invention,eliminating the need for further shaping, cutting or reforming to usethe sleeve in this invention.

Further, sleeve 62 may be used to provide bottle 64 with differentcolors, with specific designs, with colored stripes or with otherdesirable design features. For instance, sleeve 62 may be formed from aplastic differing in color from the flowing plastic conducted into moldcavity 44. Yet another embodiment could have plastic sleeve 62 formedwith stripes of differing color, printed matter and/or decorations thatare incorporated into the finished container 64, producing a prelabelledor predecorated container. Sleeve 62 may contain additives such asultraviolet light absorbers, antistatic agents, or dye receptors tofacilitate printing material or information on container 64.

While preferably liquid PET is injected into mold cavity 44 to formpreform 10, a large number of other plastics may be used in the practiceof this invention. These other materials include: polyhexamethyleneadipamide, polycaprolactam, polyhexamethylene sebacamide,polyethylene-2,6- and 1,5-naphthalate,polytetramethylene-1,2-dioxybenzoate, and copolymers of ethyleneterephthalate, ethylene isophthalate, polycarbonates, polyacrylates,polyolefins, vinyl polymer of nitrites, chlorine, styrene and othersimilar plastics polymers.

Preferably, the PET liquid is injected into mold cavity 44 at atemperature of between 500° F. to 575° F., and an internal coolant at30° F. to 110° F. is passed through the cooling passages of mold 26.Preform 10 is cooled to below about 245° F. before being removed frommold 26.

Container 64 is well suited for many purposes. For instance, asdiscussed in detail above, container 64 is especially well adapted forholding carbonated beverages. The container may be heat set to improvethe thermal stability of the container and make it suitable forpackaging products, such as fruit juices or ketchup, that are commonlyhot filled, as well as for packaging oxygen sensitive products such asbeer. Moreover, the top portions of container 64 may be trimmed to yielda completely biaxially oriented container having a cylindrical shapewith a closed end--the shape of a conventional metal can. The presentinvention is particularly well suited for forming such can-shapedcontainers because the position of the sleeve 62 can be controlledduring the molding process so that it is not later trimmed off thecontainer, maximizing the utilization of the material used to makesleeve 62.

In addition to container 64 and the modifications thereof previouslydescribed, the present invention may be effectively employed tomanufacture other useful products. For instance, the invention may beused to make a container suited for packaging foods that can be reheatedin the package using conventional or microwave ovens. Such a containercan be made by using a sleeve formed from a high gas barrier resin andinserted into a mold cavity having the shape of a can. A moltenpolycarbonate is injected into the mold cavity to form a laminatedstructure that can be used as is or subsequently expanded into anotherfinal shape. This invention may also be used to mold structures havingwindows that can function as visual level indicators for products suchas toothpaste in a pump dispenser.

The method of the present invention has several advantages compared toprocesses using multiple injections or coinjection of differingplastics. For instance, the use of sleeve 62 allows for a preciseplacement of the layer formed by the sleeve in the body of the articlebeing molded. Further, use of a relatively cool sleeve 62 reduces thetime required to cool the molten plastic conducted into cavity 44, andthus can result in increased productivity.

The process of this invention may be utilized to form laminate layers ofa wide range of thicknesses, while multiple injection processes arenormally limited to fairly thick layers. The tooling requirements andcontrol of multiple or coinjection systems are usually much more complexand expensive than what is needed for the present invention. Inaddition, as a practical matter, structures formed by multiple injectionor coinjection processes are limited to having two different plasticmaterials, while the process of this invention may be used to formstructures having more than two different plastic materials.

While it is apparent that the invention herein disclosed is wellcalculated to fulfill the objects previously stated, it will beappreciated that numerous modifications and embodiments may be devisedby those skilled in the art, and it is intended that the appended claimscover all such modifications and embodiments as fall within the truespirit and scope of the present invention.

What is claimed is:
 1. A preform for a beverage container comprising:aneck portion, a sidewall portion including an inner layer integrallyconnected to said neck portion and a bottom portion integrally connectedto said sidewall portion to form a one piece preform, said sidewallportion including a generally cylindrical pre-extruded plastic sleeveouter layer integrally bonded to said inner layer to form a preformhaving a laminated sidewall and single layer non-laminated neck andbottom portions, wherein said neck portion includes one or more threadsto receive a cap.
 2. The preform of claim 1 wherein said inner and outerlayers are made of different plastic materials.
 3. The preform of claim2 where said outer layer is made of recycled PET.
 4. The preform ofclaim 1 wherein the neck, sidewall and bottom portions are made of PET.5. The preform of claim 1 where the plastic sleeve has a low gaspermeability.
 6. The preform of claim 1 wherein the plastic sleeveincludes a lower portion that slants radially inwardly forming aconically-shaped portion.
 7. The preform of claim 1 wherein the plasticsleeve includes a lower portion that curves radially inwardly.